As for them ignoring his warning, that is their prerogative. He was honored bound to warn them. He knows they won't listen they are moronic beauracrats, who think they know better than everyone else.

The main reason for passing the occupation bill was Death Watch, his people and he are dealing with Death Watch. Satine doesn't want the Republic invading, she doesn't have the balls to lead an army to fight back the invaders, she will be forced to abandon her ways but lack the experience or even the simplest knowledge of how to lead a war. She will seek out advisers.

The Republic Senate if they pass it are handing Mandalore over to him on a bloody (as in the bodily fluid) silver plate.